Polyesters such as poly(ethylene terephthalate) (PET) are widely used in bottles and containers which are used for carbonated beverages, fruit juices, and certain foods. Useful polyesters have high inherent viscosities ("I.V.") which allow the polyester to be formed into a parison or preform and subsequently molded into a container. Because of the limited barrier properties with regard to oxygen, carbon dioxide and the like, PET containers are not generally used for products requiring a shelf life of greater than about 10 to 25 weeks. For example, oxygen transmission into PET bottles which contain beer, wine and certain food products cause these products to spoil.
It would therefore be desirable to provide improved barrier properties while retaining the I.V. necessary to form good containers from polyesters.
There are many examples in the patent literature of polyamide nanocomposites containing, for example, nylon-6 and alkyl ammonium treated montmorillonite. Some patents describe the blending of up to 60 weight percent of intercalated clay materials with a wide range of polymers including polyamides, polyesters, polyurethanes, polycarbonates, polyolefins, vinyl polymers, thermosetting resins and the like. Such high loadings with modified clays are impractical and useless with most polymers because the melt viscosity of the blends increases so much that they cannot be molded. This is especially true with polyesters. Also, clays tend to absorb large quantities of water and attempts to blend them with preformed polyesters at elevated temperatures cause severe degradation of the molecular weight of the polyester.
The following references disclose various chemically modified organoclay materials: U.S. Pat. Nos. 4,472,538; 4,546,126; 4,676,929; 4,739,007; 4,777,206; 4,810,734; 4,889,885; 4,894,411; 5,091,462; 5,102,948; 5,153,062; 5,164,440; 5,164,460; 5,248,720; 5,382,650; 5,385,776; 5,414,042; 5,552,469; WO Pat. Application Nos. 93/04117; 93/04118; 93/11190; 94/11430; 95/06090; 95/14733;
D. J. Greenland, J. Colloid Sci. 18, 647 (1963); Y. Sugahara et al., J. Ceramic Society of Japan 100, 413 (1992); P. B. Messersmith et al., J. Polymer Sci.: Polymer Chem., 33, 1047 (1995); C. O. Sriakhi et al., J. Mater. Chem. 6, 103(1996).
WO 93/04117 discloses a wide range of polymers melt blended with up to 60 weight percent of platelet particles derived from certain organoclays. Although use of polyesters is disclosed, specific polyester/platelet compositions of any molecular weight are not disclosed. WO 93/11190 describes similar polymer blends. All examples include polyamides as a polymer component.
WO 93/04118 discloses composite material of a melt processable polymer and up to 60 weight percent of platelet particles derived from organoclays. Among a wide range of thermoplastic polymers, polyesters are listed as operable. Example 6 shows the melt compounding of PET and Claytone APA (a commercial organomontmorillonite from Southern Clay Products) in a twin screw extruder to prepare a PET composite containing 0.38 weight percent platelet particles. This composite has been found to have a relatively low melt viscosity of about 5,000-12,000. There is no disclosure which would suggest how to increase the melt viscosity of the materials disclosed.
JP Kokai No. 9-176461 discloses polyester bottles wherein the polyester contains swellable laminar silicate. WO 97/31057 discloses polymer composites having dispersed therein inorganic material such as clay which is separated with an inorganic intercalant. WO 97.backslash.31973 discloses producing a composite material by mixing an organic polymer with a potassium ionomer in which the ethylene methacrylate copolymer is either partially or completely neutralized with an organic polymer. However, the foregoing references produce materials comprising very large aggregates and tactoids and little if any dispersion of individual platelet particles. Nor do any of the references disclose nanocomposite compositions having other desirable properties such as high melt strength, viscoity and I.V.
U.S. Pat. No. 5,552,469 describes the preparation of intercalates derived from certain clays and water soluble polymers such as polyvinyl pyrrolidone, polyvinyl alcohol, and polyacrylic acid. Although the specification describes a wide range of thermoplastic resins including polyesters and rubbers which can be used in blends with these intercalates, there are no examples teaching how to make such blends.
U.S. Pat. No. 4,889,885 describes the polymerization of various vinyl monomers such as methyl methacrylate and isoprene in the presence of sodium montmorillonite. In Example 11, it describes the polycondensation of dimethyl terephthalate and ethylene glycol in the presence of 33 weight percent of a montmorillonite clay in water (actually 6.2 weight % clay in the final composite). Such large amounts of clay cause quite large increases in melt viscosity and such melt phase PET samples prepared in this manner have I.V.s which are less than about 0.5 dl/g. Such low I.V. polymer would not be useful in preparing bottles.
U.S. Pat. No. 4,163,002 discloses a process for solid state polymerization of polyalkylene terepthalates fortified with 2 to 80 wt % of a filler. The preparation of compositions comprising platelet particles or of any particles with dimensions less than 1000 nm is not disclosed.